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RFC 1850 - 3.12. OSPF External Link State Database

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### 3.12. OSPF External Link State Database

    --  OSPF Link State Database, External

    --      The Link State Database contains the Link State
    --      Advertisements from throughout the areas that the
    --      device is attached to.

    --             This table is identical to the OSPF LSDB Table in
    --      format, but contains only External Link State
    --             Advertisements.  The purpose is to allow external
    --      LSAs to be displayed once for the router rather
    --      than once in each non-stub area.

        ospfExtLsdbTable OBJECT-TYPE
            SYNTAX   SEQUENCE OF OspfExtLsdbEntry
            MAX-ACCESS   not-accessible
            STATUS   current
            DESCRIPTION
               "The OSPF Process's Links State Database."
           REFERENCE
              "OSPF Version 2, Section 12  Link  State  Adver-
              tisements"
          ::= { ospf 12 }

        ospfExtLsdbEntry OBJECT-TYPE
            SYNTAX   OspfExtLsdbEntry
            MAX-ACCESS   not-accessible
            STATUS   current
            DESCRIPTION
               "A single Link State Advertisement."
           INDEX { ospfExtLsdbType, ospfExtLsdbLsid, ospfExtLsdbRouterId }
           ::= { ospfExtLsdbTable 1 }

    OspfExtLsdbEntry ::=
        SEQUENCE {
            ospfExtLsdbType
                INTEGER,
            ospfExtLsdbLsid
                IpAddress,
            ospfExtLsdbRouterId
                RouterID,
            ospfExtLsdbSequence
                Integer32,
            ospfExtLsdbAge
                Integer32,
            ospfExtLsdbChecksum
                Integer32,
            ospfExtLsdbAdvertisement
                OCTET STRING
                  }

        ospfExtLsdbType OBJECT-TYPE
            SYNTAX   INTEGER    {
                        asExternalLink (5)
                      }
            MAX-ACCESS   read-only
            STATUS   current
            DESCRIPTION
               "The type  of  the  link  state  advertisement.
               Each  link state type has a separate advertise-
               ment format."
           REFERENCE
              "OSPF Version 2, Appendix A.4.1 The  Link  State
              Advertisement header"
          ::= { ospfExtLsdbEntry 1 }

        ospfExtLsdbLsid OBJECT-TYPE
            SYNTAX   IpAddress
            MAX-ACCESS   read-only
            STATUS   current
            DESCRIPTION
               "The Link State ID is an LS Type Specific field
               containing either a Router ID or an IP Address;
               it identifies the piece of the  routing  domain
               that is being described by the advertisement."
           REFERENCE
              "OSPF Version 2, Section 12.1.4 Link State ID"
          ::= { ospfExtLsdbEntry 2 }

        ospfExtLsdbRouterId OBJECT-TYPE
            SYNTAX   RouterID
            MAX-ACCESS   read-only
            STATUS   current
            DESCRIPTION
               "The 32 bit number that uniquely identifies the
               originating router in the Autonomous System."
           REFERENCE
              "OSPF Version 2, Appendix C.1 Global parameters"
          ::= { ospfExtLsdbEntry 3 }

    --  Note that the OSPF Sequence Number is a 32 bit signed
    --  integer.  It starts with the value '80000001'h,
    --  or -'7FFFFFFF'h, and increments until '7FFFFFFF'h
    --  Thus, a typical sequence number will be very negative.
        ospfExtLsdbSequence OBJECT-TYPE
            SYNTAX   Integer32
            MAX-ACCESS   read-only
            STATUS   current
            DESCRIPTION
               "The sequence number field is a  signed  32-bit
               integer.   It  is used to detect old and dupli-
               cate link state advertisements.  The  space  of
               sequence  numbers  is  linearly  ordered.   The
               larger the sequence number the more recent  the
               advertisement."
           REFERENCE
              "OSPF Version  2,  Section  12.1.6  LS  sequence
              number"
          ::= { ospfExtLsdbEntry 4 }

        ospfExtLsdbAge OBJECT-TYPE
            SYNTAX   Integer32    -- Should be 0..MaxAge
            MAX-ACCESS   read-only
            STATUS   current
            DESCRIPTION
               "This field is the age of the link state adver-
               tisement in seconds."
           REFERENCE
              "OSPF Version 2, Section 12.1.1 LS age"
          ::= { ospfExtLsdbEntry 5 }

        ospfExtLsdbChecksum OBJECT-TYPE
            SYNTAX   Integer32
            MAX-ACCESS   read-only
            STATUS   current
            DESCRIPTION
               "This field is the  checksum  of  the  complete
               contents  of  the  advertisement, excepting the
               age field.  The age field is excepted  so  that
               an   advertisement's  age  can  be  incremented
               without updating the  checksum.   The  checksum
               used  is  the same that is used for ISO connec-
               tionless datagrams; it is commonly referred  to
               as the Fletcher checksum."
           REFERENCE
              "OSPF Version 2, Section 12.1.7 LS checksum"
          ::= { ospfExtLsdbEntry 6 }

        ospfExtLsdbAdvertisement OBJECT-TYPE
            SYNTAX   OCTET STRING (SIZE(36))
            MAX-ACCESS   read-only
            STATUS   current
            DESCRIPTION
               "The entire Link State Advertisement, including
               its header."
           REFERENCE
              "OSPF Version 2, Section 12  Link  State  Adver-
              tisements"
          ::= { ospfExtLsdbEntry 7 }

Next: 3.13. OSPF Route Table Use

Connected: An Internet Encyclopedia
RFC 1850 - 3.12. OSPF External Link State Database